3PPA stops mount tracking

[J Magill]

When exiting or terminating the 3-pt polar alignment (3PPA) plugin, NINA is sending an ASCOM instruction to the mount that stops the mount from tracking. This happened three times on one night and three times on a second imaging night. In no case did 3PPA terminate without stopping the mount from tracking. My mount is a Losmandy GM811G running Gemini Telescope.net I am running NINA 2.0 with 3PPA version 1.7.0.0 I can supply the ASCOM log if that would help. – Jim

[Marc Blank]

I believe this is expected behavior.

[J Magill]

This may be the way the plug-in was designed but it surely is not expected behavior from a users perspective. I know of no other operation in NINA that results in tracking stopping. And there is no warning given by NINA and nothing in the written summary of the plug-in. What possible use is there to stop the tracking? If there is some special case that requires it, then add an option to turn that feature on or off.

[Dale Ghent]

Due to the way that TPPA drives the mount, the axes can end up in an unsafe configuration if the user initiates the process from angles that move the scope beyond any skewing or tracking limits. Because there is no way for an app to know that these limits are present or what they are, as these are driver-enforced constructs and there is no programmatic interface to be able to know this, it’s a safety feature to keep tracking off. It needs to be off for the alignment process and is kept that way. It is intended that the user reenables tracking once they are satisfied with the alignment and has verified that the axes are not left in a precarious state, or has had the opportunity to move them to a safe or desired orientation.

You can easily turn tracking on manually in the UI, and of course in a sequence.

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[Stefan B]

Dale, during alignment tracking is required to be on. However the rest is correct. After alignment there is no need to risk pier collision and tracking is not required anymore.

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Furthermore any slew to RA/Dec coordinates will enable tracking again anyways, so what is the problem to have it turned off?

[J Magill]

My workflow for initiating an imaging session is to polar align and then check the orientation of the camera. So I first encountered the tracking being off when plate solving failed when checking the camera orientation. Next workflow step is to calibrate guiding. Neither of these two steps require a slew and so are victims of tracking being off. My mount has safety limits so there is never a need for tracking to be off. The solution is obvious. Add a user option to end 3PPA with tracking on or with tracking off. The default can be tracking off. But even in the tracking off case I think a warning message to the user that tracking has been turned off would be a useful courtesy.

[Dale Ghent]

Assuming you don’t have a motorized rotator, you can check the camera orientation against your target in the sequence by using the Manual Rotator device. There’s no need to do that out of band.

Safety limits and their type also vary from mount to mount. In the vast majority of drivers, the way that TPPA moves the axes is not stopped by mount limits, which pertain to commanded slews to a specific coordinate and/or during tracking. MoveAxis commands generally aren’t covered by mount limits, hence the caution being taken here. There’s no need to press this issue; this is intended and tracking can be easily restored either manually or via slew to a RA/Dec coordinate (as slews to a RA/Dec require tracking to be on anyhow, per the ASCOM specification.)

[Stefan B]

Latest version has a toggle to keep tracking. Use with caution to not run into pier crashes.